PTFE Open Adjustment Coupler Spacer and Riser for MMU - Magnetically Soft Joined

This is a key part of my MCS (multicolor system) -  https://www.printables.com/model/555238-mcs-multi-color-system-for-prusa-mmu

See how this works here  - https://www.youtube.com/shorts/H3z1xf8s-6c

This coupler/stand combo replaces earlier designs (air buffer, polybox, larger footprints similar to this) and is core part of an MMU system I made.  This is  more compact setup with a shorter filament path and less friction. Although you can use this as you like in your own setup, ideally you should use these as I outline here, specifically as shown in the second picture. 

I have been designing my MMU setup and in particular the filament path behind the MMU combined with a slot buffer behind this. and finally some frictionless spools.

See my collection called used on MMU Now and Works to see all mods I am using, this being one of them.

Short spacer bar  - https://www.printables.com/model/460874

Riser and couplers - https://www.printables.com/model/432647

PTFE Adapter connectors - https://www.printables.com/model/416215

PTFE Angle bracket - https://www.printables.com/model/470374

 This coupler/stand combo has three purposes:

• The coupler opening allows you to adjust and feel the filament loading, retraction, etc, and lets you to push the filament forward when loading initially
• The stand and coupler together form a small hill that traps the filament against the walls of the tubes so it doesn't slide backwards or forwards after the idler puts it in position. This filament pathway shape is determined by the position of the coupler, the length of tubing, and the distance to the MK3 back frame. All three of these need to look like that picture to get the right amount of filament stress against the PTFE walls to prevent load errors
• The couplers have magnets on their sides and stay together that way. Only the center one fits in a slot on the riser. Because they can be easily seperated, this allows you to move them around independently as you load the filament or buffer behind and not put a bend in your tubing while doing so. ALthough the main pic shows two spacers, only use one PTFE spacer. Put it between the coupler and the MMU, in order to allow this easy seperation around the slot buffer loading area as you pull out slots to load them.

Here are the positioning dimensions :

1. The stand is attached to a  platform (a board that you need to make) in 3D space 10.5-11 inches behind the MK3 back metal lower frame, and the top of the board is 11.5-12 inches high. 
2. The 5 tubes between the coupler and MMU are 3mm inner diameter 4mm outer diameter tubes (not the 2mm inner diameter ones that came with the printer as those add too much friction).  Theses five tubes above are exactly the same as the stock tube between the MMU and extruder, with about half an inch added as well. in order to enforce the  S shape.
3. The position of the printer should form an S curve shape of the filament path. 
4. The couplers should ideally have 1x10 magnets superglued to all sides so the click together. 
5. One PTFE spacer comb of your choice is used between the coupler and MMU, and is positioned a little closer to the coupler. I have  spacer in my collection but you can any 5 hole 15mm spaced PTFE tube spacer. 
6. There is another optional part I uploaded here called PTFE_spacer bracker. This can be mounted between the riser and the MMU and you want to superglue it to the spacer comb to lock the PTFE tubes into position in 3D space. 
7. The PTFE tube route behind this should be about the angle of the image and ideally go to a buffering system of your choice.

How to Tune the Positioning Further

When you have it all setup try pulling the filament manually out of the front PTFE tubes. It should come out with only a little effort. If too much effort then there is too much friction in your setup. If it is no effort and you think it might slip then add static friction by moving the printer backwards more to make an even more curved S shape until there is just enough friction to prevent the filament from moving in the tube by itself.

It is up to you to build this platform and use a buffer of your choice behind the coupler. I amm using  a slot buffer and you can see an optimal short filament path between all those elements. All the tubes are 3mm inner diameter in the setup now (including the short ones inside the MMU between the idler and selector, and the tube between the selector and extruder). You can see my frictionless spool design in my collection too. PC4M10 jacks are used everywhere, 32 of them in fact.

Also, pay attention to the polarity of the magnets so they can all connect as a unit.

The Risers come in a few different styles and heights. I am using the 96mm one in my setup. Also use the PTFE spaver bracket with a spacer glued to it to to lock the tubes in 3D space between the riser and the MMU. 

If the  riser isn't the height you want you can adjust the height in Prusaslicer this way of the middle section this way!  Place the riser on its side cut it at a 270 angle (vertically) into parts. Then slide the parts closer if you want it shorter. If you want it larger you need to insert a part that is a block and resize it to fit (4mm wide, 40 tall) the gap.

7/22/2023 - improved the  coupler part (compler_MC4M10_improved.stl):

• longer threaded length on the ends so the PC4M10 jack can be fully screwed in
• larger hole so the filament can more easily go through it
• filleted inner sides for strength
• redid the threads into the part to make sure they were done correctly